chromium/third_party/blink/web_tests/animations/resources/keyframes.css

@-webkit-keyframes anim {
    from { left: 50px; }
    20%  { left: 100px; }
    40%  { left: 100px; }
    60%  { left: 200px; }
    80%  { left: 200px; }
    to   { left: 300px; }
}